An airplane is moved by several turbojet engines each housed in a nacelle also housing a set of related actuating devices connected to its operation and performing various functions when the turbojet engine is operating or stopped. These related actuating devices in particular comprise a mechanical system for actuating thrust reversers.
As shown in FIG. 1, a nacelle 1 generally has a tubular structure comprising an air intake 2 upstream of the turbojet engine, a middle section 3 designed to surround a fan of the turbojet engine, a downstream section 4 housing thrust reverser means and designed to surround the combustion chamber of the turbojet engine, and generally ends with jet nozzle 5, the outlet of which is located downstream of the turbojet engine. Modern nacelles are designed to house a turbofan engine capable of generating, via internal blades of the body of the engine, a hot air flow (also called primary flow) coming from the combustion chamber of the turbojet engine, and via the fan blades, a cold air flow (secondary flow) that circulates outside the turbojet engine through an annular channel 6, also called stream, formed between a fairing of the turbojet engine 7 and an internal structure 8 of the nacelle. The two air flows are ejected from the turbojet engine through the rear of the nacelle 1.
The role of a thrust reverser is, during landing of an aircraft, to improve the braking capacity thereof by reorienting at least part of the thrust generated by the turbojet engine forward. In this phase, the reverser obstructs the stream of the cold flow and orients it towards the front of the nacelle, thereby creating a counter-thrust that is added to the braking of the airplane's wheels.
The means implemented to perform this reorientation of the cold flow vary depending on the type of reverser.
However, in any case, the structure of a reverser comprises elements that can be moved between, on one hand, a deployed position in which they open, in the nacelle, a passage for the deflected flow, and on the other hand, a retracted position in which they close said passage. These cowls can perform a deflecting function or simply activate other deflecting means.
A reverser of the prior art is illustrated in FIGS. 2 and 3. This reverser is of the vane reverser or cascade vane reverser type.
This type of reverser includes at least one cowl 9 that can move relative to a stationary structure 15, said cowl 9 having an outer wall 17 and an inner wall 10 intended to define, in a direct jet position of the turbojet engine (FIG. 2), an outer wall of the annular channel 6 in which the secondary flow flows. The reverser also includes at least one flap 11 pivotably mounted on the mobile cowl 9 and actuated by at least one connecting rod 12 when the mobile cowl is moved downstream, such that, in a thrust-reversal position (FIG. 3), each flap 11 includes a zone extending in the annular channel 6 so as to at least partially deflect the secondary flow outside said annular channel 6.
In the case of this type of reverser, the reorientation of the secondary flow is done by cascade vanes 13, the mobile cowl 9 simply serving for sliding aiming to expose or cover said vanes, the translation of the mobile cowl 9 being done along a longitudinal axis substantially parallel to the axis of the nacelle 1.
A housing 14 is formed in the mobile cowl 9 and makes it possible to house the vanes 13 when the reverser is not actuated, i.e. in the direct jet position, as shown in FIG. 2.
The vanes 13 are arranged adjacent to each other, in an annular zone surrounding the annular channel 6, the vanes 13 being arranged edge to edge so that no space is formed between them. In this way, the entire secondary flow deflected by the flaps 11 passes through the vanes 13. The means for moving and guiding the mobile cowl (not shown) is arranged under the vanes 13.
Another reverser of this type is shown diagrammatically in FIG. 4. In that figure, elements having the same function as before have been designated using the same references.
This reverser does not have a deflection flap 11. The cowl 9 is mounted so as to be able to move relative to a stationary part, called front frame 15. The cowl 9 includes an inner wall 10, defining a peripheral wall of the annular channel 6 and an outer wall 17 aligned with an outer wall 18 of the front frame 15.
The front frame 15 includes a rounded deflection edge 19 extending from the periphery of the annular channel 6 to the upstream end of the vanes 13.
The nacelle includes an internal structure 8 defining the inner wall of the annular channel 6 and having a wider zone 20 of the diameter of said internal structure 8. The annular channel then forms an S-shaped stream. The free end 43 of the inner wall 16 of the mobile cowl 9 is aligned with or close to said wider zone 20, in the thrust reversal position (FIG. 6). In this way, the secondary flow F flowing in the annular channel 6, from upstream to downstream, is blocked by the inner wall 16 of the cowl, then escapes towards the outside, through the deflection vanes 13.
For efficiency reasons, the deflection edge 19 must have a large curve radius. Moreover, in order to be able to maximally increase the length of the vanes 13 so as to maximally deflect the secondary flow F in the upstream direction, it is necessary to arrange the vanes 13 as close as possible to the outer wall 17 of the cowl 9. The limited length of the housing of the mobile cowl 9 and the large radius of the deflection edge 19 result in reducing the length of the vanes 13.
In order to offset this drawback, it is known to arrange the vanes at an angle. The set of vanes then extends like a cone section, around the annular channel.
Document EP 1 229 237 describes such a reverser, in which the vanes are arranged at an angle. In this case, however, it is no longer possible to arrange the means for moving and guiding the mobile cowl under the vanes. The vanes are then spaced apart from each other so that the aforementioned movement and guiding means is arranged between two adjacent vanes.
In that case, part of the secondary flow can escape into the space formed between the vanes, which results in decreasing the deflection of the secondary flow and therefore the effectiveness of the reverser.